1. Field of the Invention
The present invention relates to a small scale explosive testing apparatus and method. More particularly, the small scale explosive testing apparatus of the present invention is reusable.
2. Brief Description of the Related Art
Non-ideal underwater explosives usually contain a significant portion of slow reacting componentsxe2x80x94for example, a mixture of aluminum and ammonium perchlorate particles. Only a fraction of the explosive""s energy is released early enough to contribute to sustaining the detonation front which, therefore, propagates at lower velocity and pressure than in ideal explosives. The slow-reacting components release the remaining energy late, after the Chapman-Jouguet (CJ) surface, often even after the bubble has expanded several times the volume of the charge.
The slow release of energy poses a challenge for conventional testing methods. The detonation products have to remain longer at high temperature and pressure in order to allow the non-ideal components enough time to react. This is accomplished by either using a large explosive charge or by confining the detonation products. In underwater tests, the inertial resistance of the water helps slow the expansion of the products, but because the bubble expands in all directions, the resulting spherical divergence quickly reduces the pressure and temperature inside.
Typical underwater explosives are non-ideal and therefore characterized by their late-time energy release. In order for late-time reactions to occur, the reaction products have to be maintained together under high pressure for periods on the order of several milliseconds. Small-Scale tests such as the Moby-Dick test can observe late-time reactions, but cannot reach high pressures, such as approximately 1 kbar, which are required to evaluate the rates and pressure dependencies of the late-time reactions. In the Moby-Dick test, the bubble expansion is restricted to one-direction only in order to reduce the divergency and slow the rate of pressure decay.
Large scale explosive evaluation shots, typically between 50 and 100 kg, are carried out underwater in quarries to evaluate this late-time performance under high pressure since the product gases are held together due to the inertial confinement of the water. However, these large scale shots are expensive and difficult to instrument.
Explosive and pressure containment systems have been disclosed in several patents. U.S. Pat. No. 1,068,904 to Ionides, Jr. discloses a means for preventing the backward propagation of a flame along a conduit. U.S. Pat. No. 2,335,779 to Mazzei discloses a casing for carriers for nitro-glycerin which may be filled with water. U.S. Pat. No. 2,673,660 to Nordin discloses a pressure relief device having a tubular body. U.S. Pat. No. 3,268,107 to Sperling discloses a container for hazardous material having cylindrical sidewalls and a domed or partially spherical top surface. U.S. Pat. No. 3,367,490 to Jensen, et al. discloses a container for free flowing materials. U.S. Pat. No. 3,434,336 to Harr discloses an explosion barrier having foam to prevent an explosion from spreading between two chambers. U.S. Pat. No. 3,820,435 to Rogers, et al. discloses a spherical walled containment vessel with a plurality of access ports that is evacuated to a pressure of about 500 microns. U.S. Pat. No. 4,174,624 to Shrun, U.S. Pat. No. 5,833,782 to Crane, et al., and U.S. Pat. Nos. 5,613,453 and 5,884,569 to Donovan disclose apparatuses for explosion containment.
Explosive testing devices also have been disclosed in several patents. U.S. Pat. No. 4,300,962 to Stinecipher, et al. discloses an aquarium test defined by detonating a cylindrical charge in a plexiglass aquarium filled with water. U.S. Pat. No. 4,110,136 to Hershkowitz, et al. discloses a tube for a confined small-scale detonation velocity and dent test with a steel cylinder. U.S. Pat. No. 4,932,239 to Regalbuto discloses a testing apparatus employed to test explosive charges.
Drafted documents entitled xe2x80x9cA Closed Water-Filled Cylinder Test for Characterizing Non-Ideal Explosivesxe2x80x9d by R. Guirguis, et al., Naval Surface Warfare Center, Indian Head, Md., 97 APS Paper; xe2x80x9cA Closed Water-Filled Cylinder to Characterize Non-Ideal Explosivesxe2x80x9d R. Guirguis, et al., Naval Surface Warfare Center, Indian Head, Md., 11th Det. Symposium; and xe2x80x9cA Closed Water-Filled Cylinder Test for Characterizing Non-Ideal Explosivesxe2x80x9d by R. Guirguis, et al., Naval Surface Warfare Center, Indian Head, Md., 97 JANNAF PSHS, the disclosures of which are herein incorporated by reference, describe several aspects of small-scale explosive testing.
Although in the above identified patents and references several explosive containment or testing devices are disclosed, none of the patents discloses a reusable small scale testing apparatus for non-ideal explosives. The present invention addresses this and other needs.
The present invention includes a reusable small-scale explosive testing apparatus comprising a structural member having a closed end and a receiving end forming a hollow cylindrical chamber therein, the chamber having a curved radius internal surface at the closed end and the chamber extending through the structural member at the receiving end, the chamber further having a substantially constant radius along the length of the structural member, the receiving end having an externally threaded circumference thereon, a head piece having an insertion component and covering component, wherein the insertion component fits into the chamber on the receiving end and partially fills the chamber, the covering component resting adjacent to the receiving end, a cap forming a cavity therein configured to receive the head piece, the cavity further forming internally threaded surface for mating with the externally threaded circumference of the structural member, a gage configured for units of pressure versus time measurements, a confinement liquid component of sufficient volume to fill the chamber for testing and means for releasing pressure extending from the structural member through the head piece and cap, wherein the means for releasing pressure is capable of retaining and releasing high pressures from the structural member.
The present invention also includes a method for small-scale explosive testing, comprising the steps of providing a reusable small-scale explosive testing apparatus comprising a structural member having a closed end and a receiving end forming a hollow cylindrical chamber therein, the chamber having a curved radius internal surface at the closed end and the chamber extending through the structural member at the receiving end, the chamber further having a substantially constant radius along the length of the structural member, the receiving end having an externally threaded circumference thereon, a head piece having an insertion component and covering component, wherein the insertion component fits into the chamber on the receiving end and partially fills the chamber, the covering component resting adjacent to the receiving end, a cap forming a cavity therein configured to receive the head piece, the cavity further forming internally threaded surface for mating with the externally threaded circumference of the structural member, a gage configured for units of pressure versus time measurements, a confinement liquid component of sufficient volume to fill the chamber for testing and means for releasing pressure extending from the structural member through the head piece and cap, wherein the means for releasing pressure is capable of retaining and releasing high pressures from the structural member, inserting a sample amount of explosive into the chamber, filling the chamber with the confinement liquid, fitting the headpiece onto the receiving end of the structural member, screwing the cap onto the structural member, detonating the explosive sample, measuring the resulting high pressure of the detonated explosive sample, and releasing the high pressure from within the chamber.
Additionally, the present invention includes a pressure evaluation product produced by the process comprising the steps of providing a reusable small-scale explosive testing apparatus comprising a structural member having a closed end and a receiving end forming a hollow cylindrical chamber therein, the chamber having a curved radius internal surface at the closed end and the chamber extending through the structural member at the receiving end, the chamber further having a substantially constant radius along the length of the structural member, the receiving end having an externally threaded circumference thereon, a head piece having an insertion component and covering component, wherein the insertion component fits into the chamber on the receiving end and partially fills the chamber, the covering component resting adjacent to the receiving end, a cap forming a cavity therein configured to receive the head piece, the cavity further forming internally threaded surface for mating with the externally threaded circumference of the structural member, a gage configured for units of pressure versus time measurements, a confinement liquid component of sufficient volume to fill the chamber for testing and means for releasing pressure extending from the structural member through the head piece and cap, wherein the means for releasing pressure is capable of retaining and releasing high pressures from the structural member, inserting a sample amount of explosive into the chamber, filling the chamber with the confinement liquid, fitting the headpiece onto the receiving end of the structural member, screwing the cap onto the structural member, detonating the explosive sample, measuring the resulting high pressure of the detonated explosive sample, and releasing the high pressure from within the chamber.
The small-scale tests provide detonation products of an explosive that are confined at high pressure in a closed cylinder completely filled with water. Numerical simulations of the test show that although the dynamic effects of the shock induced into the water reduce the pressure below the theoretical maximum achievable if all processes were quasi-static, the residual equilibrium pressure is still high enough for the slow reactions of non-ideal explosives to proceed at a finite measurable rate.